Ignition coil assemblies used in the automotive industry have in the past been placed where there is enough space to contain the size and shape of the coil assembly. Long wires are used to connect to spark plugs. This creates losses in the wires and unnecessary size and weight under the hood.
The ignition coil assembly is directly applied to the spark plug or attached very near to the spark plug. This patent describes an improved method for producing the core of such coil assembly.
This present invention relates to an effective cost efficient process to produce the core in an ignition coil assembly that is fastened directly onto the spark plug or mounted very near the plug of an internal combustion engine.
Typically, the ignition cores have been produced with thin lamination or powdered iron with a thin layer of polymer coating over each particle of iron. (See U.S. Pat. No. 5,211,896).
The powdered iron particles with thin layers of polymer and/or the thin laminations are used to carry magnetic flux. The polymer and/or resin coatings over each particle are used to reduce eddy current losses, as are the sheets of lamination. These losses occur in AC and pulse DC applications.
When attaching the ignition coil assembly directly onto the spark plug or mounting near the plug, a cylindrical design is the most space efficient. Reduction in size is a very important design feature for under hood applications in future automobiles.
Flat laminations do not lend themselves to circular design, and powdered iron with microencapsulated polymers uniaxially compacted typically do not have as high a flux carrying capacity due to lower density (6.90-7.4 gm/cc) or commonly called percent of fill (88-94%).
Previous attempts to achieve 99% theoretical density on powdered metal have resulted in high core losses due to breakdown of coated layer. Two examples of these attempts are pneumatic forging and the Ceracon process (trademark of Ceracon, Inc.).
The trend in the automotive ignition industry is for a smaller coil assembly which can be placed closer to the spark plug or integrated into the spark plug design. The core, as well as the coil assembly, needs to be smaller and also more efficient.
Currently, most cores for AC electromagnetic ignition application utilize either a laminated core or a composite iron core pressed by uniaxial compaction. The laminated cores have fairly good magnetic properties but are expensive to produce and have a limited application because of restricted design flexibility and dimensional tolerance capabilities. The sharp edges produced during blanking may cause primary wire grounds on cylindrical designs. The uniaxial composite iron cores also have fairly good magnetic properties, but are limited to a medium density because of the lack of compressibility of the composite iron powder and uniaxial molding process. If the composite iron core is compacted in the horizontal direction, burrs at the parting lines which run along with length of the part, cause reduced dimensional accuracy and winding grounds. This often requires a secondary grinding process to overcome these problems, which adds costs to the process.
Other patents of interest include U.S. Pat. No. 5,405,574; U.S. Pat No. 5,472,661 and U.S. Pat. No. 5,629,092.